U.S. patent number 7,753,036 [Application Number 11/824,645] was granted by the patent office on 2010-07-13 for compound cycle rotary engine.
This patent grant is currently assigned to United Technologies Corporation. Invention is credited to Arindam Dasgupta, Roy N. Guile, Jonathan Lauter, Charles E. Lents, Vincent C. Nardone, Stephen P. Zeppieri.
United States Patent |
7,753,036 |
Lents , et al. |
July 13, 2010 |
Compound cycle rotary engine
Abstract
A compound cycle engine system has a rotary engine, which rotary
engine generates exhaust gas. The system further has a compressor
for increasing the pressure of inlet air to be supplied to the
engine to a pressure in the range of from 3.0 to 5.0 atmospheres
and an intercooler for providing the inlet air to the engine at a
temperature in the range of from 150 to 250 degrees Fahrenheit. The
system further has one or more turbines for extracting energy from
the exhaust gas. The Miller Cycle is implemented in the rotary
engine, enabling the compression ratio to be lower than the
expansion ratio, allowing the overall cycle to be optimized for
lowest weight and specific fuel consumption.
Inventors: |
Lents; Charles E. (Amston,
CT), Zeppieri; Stephen P. (Glastonbury, CT), Guile; Roy
N. (Wethersfield, CT), Nardone; Vincent C. (South
Windsor, CT), Lauter; Jonathan (Great Neck, NY),
Dasgupta; Arindam (West Hartford, CT) |
Assignee: |
United Technologies Corporation
(Hartford, CT)
|
Family
ID: |
39816967 |
Appl.
No.: |
11/824,645 |
Filed: |
July 2, 2007 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090007882 A1 |
Jan 8, 2009 |
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Current U.S.
Class: |
123/559.1 |
Current CPC
Class: |
F02B
53/04 (20130101); F02B 37/00 (20130101); F01C
11/008 (20130101); F01C 1/22 (20130101); F02B
41/10 (20130101); F02B 29/0437 (20130101); Y02T
10/12 (20130101); Y02T 10/144 (20130101); Y02T
10/17 (20130101); Y02T 10/163 (20130101); Y02T
10/142 (20130101); F02B 2275/32 (20130101) |
Current International
Class: |
F02B
33/00 (20060101) |
Field of
Search: |
;123/559.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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55153820 |
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Dec 1980 |
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JP |
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02211318 |
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Aug 1990 |
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JP |
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07091265 |
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Apr 1995 |
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JP |
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Primary Examiner: Denion; Thomas E
Assistant Examiner: Davis; Mary A
Attorney, Agent or Firm: Bachman & LaPointe, P.C.
Claims
What is claimed is:
1. A compound cycle engine system comprising: a rotary engine
having a displacement of from 1 to 10 liters, said rotary engine
generating exhaust gas; said rotary engine being operated so that
intake and exhaust pressures are within 0.5 atmospheres; said
rotary engine having an intake port and an exhaust port; said
intake and exhaust ports being arranged so that said engine has a
cycle in which an internal expansion volume is greater than an
internal compression volume; means for supplying inlet air at a
pressure in the range of from 3.0 to 5.0 atmospheres and a
temperature in the range of from 150 to 250 degrees Fahrenheit to
said rotary engine; said air supplying means comprising a
compressor; a first turbine connected to the compressor by a shaft,
said first turbine receiving said exhaust gas from said engine and
reducing exhaust gas pressure; a second turbine having an output
shaft, said second turbine receiving said exhaust gas and having an
expansion ratio in the range of 2.0:1 to 7.0:1; and said engine
having a power shaft and said output shaft of said second turbine
being connected to said power shaft.
2. The compound cycle engine system according to claim 1, wherein
said compressor raises the pressure of said inlet air to said 3.0
to 5.0 atmospheres and said air supplying means further comprises
an intercooler for receiving said inlet air at said raised pressure
from said compressor and for lowering the temperature of said inlet
air to said 150 to 250 degree Fahrenheit range.
3. The compound cycle engine system according to claim 1, wherein
said output shaft is connected to said power shaft via a gear
arrangement.
4. The compound cycle engine system according to claim 1, wherein
said intake port opens at 0 to 15 degrees after top dead center and
closes at 115-140 degrees after bottom dead center.
5. The compound cycle engine system according to claim 1, wherein
said compressor has a compression ratio in the range of from 3.0:1
to 5.0:1.
6. The compound cycle engine system according to claim 1, wherein
said rotary engine has a cooling system which operates at a
temperature up to 250 degrees Fahrenheit.
7. The compound cycle engine system according to claim 1, wherein
said rotary engine maintains a peak cycle pressure in the range of
from 1200 to 1800 psia.
8. The compound cycle engine system according to claim 1, wherein
said exhaust gas has a temperature in the range of from 1500 to
1800 degrees Fahrenheit.
9. The compound cycle engine system according to claim 1, wherein
said exhaust gas has a pressure in the range of from 3.0 to 5.0
atmospheres.
10. A compound cycle engine system comprising: a rotary engine,
said rotary engine generating exhaust gas; means for supplying
inlet air at a pressure in the range of from 3.0 to 5.0 atmospheres
and a temperature in the range of from 150 to 250 degrees
Fahrenheit to said rotary engine; said air supplying means
comprising a compressor; means for extracting energy from said
exhaust gas; said energy extracting means comprising a first
turbine connected to the compressor by a shaft which receives said
exhaust gas from said engine; said energy extracting means
comprising a second turbine having an output shaft, said second
turbine receiving said exhaust gas from an outlet of said first
turbine, and said second turbine has an expansion ratio in the
range of 2.1:1 to 7.0:1; said engine has a power shaft and said
output shaft being connected to said power shaft; said rotary
engine being a Miller cycle rotary engine; said rotary engine
having an intake port and an exhaust port; said intake and exhaust
ports being arranged so that said engine has a cycle in which an
internal expansion volume is greater than an internal compression
volume; said engine having an intake port which opens opening at 0
to 15 degrees after top dead center and which closes closing at
115-140 degrees after bottom dead center; and said engine having an
exhaust port which opens opening at 70 to 90 degrees before bottom
dead center.
11. The compound cycle engine system according to claim 10, wherein
said exhaust port closes at 38 to 65 degrees after top dead
center.
12. The compound cycle engine system according to claim 10, wherein
said rotary engine has a displacement in the range of 1.0 liter to
10 liters.
13. A vehicle having a propulsion system, which propulsion system
comprises a compound cycle engine system comprising: a rotary
engine having a displacement of from 1 to 10 liters, said rotary
engine generating exhaust gas; said rotary engine being operated so
that intake and exhaust pressures are within 0.5 atmospheres; said
rotary engine having an intake port and an exhaust port; said
intake and exhaust ports being arranged so that said engine has a
cycle in which an internal expansion volume is greater than an
internal compression volume; means for supplying inlet air at a
pressure in the range of from 3.0 to 5.0 atmospheres and a
temperature in the range of from 150 to 250 degrees Fahrenheit to
said rotary engine; said air supplying means comprising a
compressor; means for extracting energy from said exhaust gas; said
energy extracting means comprising a first turbine connected only
to the compressor by a shaft, which said first turbine receives
said exhaust gas from said engine; said energy extracting means
comprising a second turbine having an output shaft, said second
turbine receiving said exhaust gas from an outlet of said first
turbine, and said second turbine has an expansion ratio in the
range of 2.1:1 to 7.0:1; and said engine has a power shaft and said
output shaft being connected to said power shaft.
14. The vehicle according to claim 13, wherein said compressor
raises the pressure of said inlet air to said 3.0 to 5.0
atmospheres and said air supplying means further comprises an
intercooler for receiving said inlet air at said raised pressure
from said compressor and for lowering the temperature of said inlet
air to said 150 to 250 degree Fahrenheit range.
15. The vehicle according to claim 13, wherein said output shaft is
connected to said power shaft via a gear arrangement.
16. The vehicle according to claim 13, wherein said intake port
opens at 0 to 15 degrees after top dead center and closes at
115-140 degrees after bottom dead center.
17. The vehicle according to claim 16, wherein said exhaust port
opens at 70 to 90 degrees before bottom dead center.
18. The vehicle according to claim 17, wherein said exhaust port
closes at 38 to 65 degrees after top dead center.
19. The vehicle according to claim 13, wherein said compressor has
a compression ratio in the range of from 3.0:1 to 5.0:1.
20. The vehicle according to claim 13, wherein said rotary engine
has a cooling system which operates at a temperature up to 250
degrees Fahrenheit.
21. The vehicle according to claim 13, wherein said rotary engine
maintains a peak cycle pressure in the range of from 1200 to 1800
psia.
22. The vehicle according to claim 13, wherein said exhaust gas has
a temperature in the range of from 1500 to 1800 degrees
Fahrenheit.
23. The vehicle according to claim 13, wherein said exhaust gas has
a pressure in the range of from 3.0 to 5.0 atmospheres.
24. The vehicle according to claim 13, wherein said vehicle
comprises an aircraft.
25. The vehicle according to claim 13, wherein said vehicle
comprises a rotorcraft.
26. The vehicle according to claim 13, wherein said vehicle
comprises a ground vehicle.
27. The vehicle according to claim 13, wherein said vehicle
comprises a watercraft.
Description
BACKGROUND
(1) Field of the Invention
The present disclosure relates to a compound cycle rotary engine
that offers low specific fuel consumption at high power to weight.
The compound cycle rotary engine has particular utility for
propulsion systems.
(2) Prior Art
Gas turbine engines in the 500 to 3000 shaft horsepower range are
well known for having very high power to weight (power produced per
unit weight), but at high specific fuel consumption (fuel flow rate
per unit power, SFC). Intermittent combustion engines (e.g. spark
ignition, or SI, reciprocating engines and compression ignition, or
CI, reciprocating engines) are well known for having low SFC, but
at low power to weight. It is desirable to achieve low SFC at high
power to weight. A compound engine cycle which combines certain
features of both engine types has the potential to achieve low
specific fuel consumption at relatively high power to weight.
Compound engine cycles are well documented in the literature and
textbooks. In a typical compound cycle engine, energy is extracted
from the exhaust stream of a reciprocating engine by expanding the
exhaust gas through a turbine. The turbine drives a shaft that is
linked through a gearbox or fluid coupling to the main engine
output shaft, thus increasing the total system power output. The
reciprocating engine is typically otherwise conventional in nature
and may be either a CI or SI engine. In addition to the compound
cycle turbine, conventional turbochargers may be fitted in
essentially the same manner as they are to non-compound cycle
engines. Turbochargers are used to increase the power and/or
efficiency of an engine. Intercoolers may also be fitted to
increase charge density and/or control combustion temperatures.
Variations on this configuration are also well documented.
Previous attempts have been made to develop a compound cycle engine
(CCE) utilizing a compression ignition (CI) reciprocating engine
core. While these engines have been successful in achieving low
SFCs (around 0.33 lbm/hr/hp), they have not achieved high power to
weight (exceeding 2.0 hp/lbm). This is due primarily to the
reciprocating masses (pistons), valves and combustion systems
inherent in a CI engine that limits the engine's ability to operate
at high speed. The higher the engine operating speed, the more
power that can be produced for a given volume and thus the higher
the power to weight. Also, the chamber pressures and temperatures
at which CI engines operate require heavy structures for
containment.
Thus, there remains a need for a compound cycle engine which is
capable of achieving low specific fuel consumption at relatively
high power to weight.
SUMMARY
There is provided a compound cycle engine system which is capable
of achieving low specific fuel consumption at relatively high power
to weight. The compound cycle engine system broadly comprises a
rotary engine, which rotary engine generates an exhaust gas, means
for supplying inlet air at a pressure in the range of from 3.0 to
5.0 atmospheres and a temperature in the range of from 150 to 250
degrees Fahrenheit to the rotary engine, and means for extracting
energy from the exhaust gas from the rotary engine.
Other details of the compound cycle rotary engine system, as well
as other objects and advantages attendant thereto, are set forth in
the following detailed description and the accompanying drawing
wherein like reference numerals depict like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of a compound cycle rotary
engine; and
FIG. 2 is a sectional view of a rotary engine which may be used in
the compound cycle rotary engine of FIG. 1.
FIG. 3 is a schematic representation of an alternative compound
cycle rotary engine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Referring now to FIG. 1, there is shown a compound engine cycle 10
which includes a turbocharger 12 that receives air from an inlet
14. The turbocharger 12 includes a compressor 16 and a turbine 18
which are connected by a shaft 20. The compressor 16 may be a
single- or multiple-stage centrifugal device and/or an axial
device. The air from the inlet 14 flows into the compressor 16. The
compressor 16 preferably increases the pressure of the air flow to
a level in the range of from 3.0 to 5.0 atmospheres.
The air exiting the compressor 16 flows into an intercooler 22
where the temperature of the air is lowered to a relatively low
level, i.e. the air exiting the intercooler 22 and entering the
inlet of a rotary engine 24 is in the range of from 150 to 250
degrees Fahrenheit. As a result of passing the inlet air through
the compressor 16 and the intercooler 22, a very high density inlet
air can be supplied to the inlet of the rotary engine 24. A rotary
engine 24 with such high inlet air density can produce high power
in a small engine volume. The rotary engine 24 may be any suitable
rotary engine known in the art. For the desired range of
horsepower, i.e. 500 to 3000 hp, the rotary engine displacement may
range from 1 liter to 10 liters. It should be noted that
conventionally turbocharged engines of these displacements would
produce less than half the power of the proposed engine cycle
10.
The exhaust gas exiting the rotary engine 24 is supplied to two
turbines, a compressor turbine 18 and a power turbine 26, the
turbines being either in series or in parallel. In the series
arrangement, exhaust gas flows first through one of the two
turbines where the pressure is reduced, and then through the other
turbine, where the pressure is further reduced. In the parallel
arrangement, as shown in FIG. 3, the exhaust gas is split and
supplied to each turbine 18, 26 at same pressure and the pressure
is reduced by the same amount in each turbine. The series
arrangement is shown in FIG. 1. Energy is extracted from the
exhaust gas by the compressor turbine 18 and may be used to drive
the compressor 16 via the shaft 20. Energy is extracted from the
exhaust air flow by the power turbine 26 and may be used to drive
an output shaft 28. The output shaft 28 may be connected via a gear
system 30 to a shaft 32 connected to the rotary engine 24. The
combined output on shaft 32 may be used to provide propulsive power
to a vehicle application into which the engine is integrated. This
power may be delivered through a gearbox (not shown) that
conditions the output speed of the shaft 32 to the desired speed on
the application. Alternatively, the output shaft 28 may be used to
provide power to an electric generator (not shown) while the shaft
32 may be used to provide propulsive power to a vehicle
application. In yet another alternative, both output shafts 28 and
32 may be used to drive separate electric generators. Exhaust gas
exiting the turbines may be discharged in any suitable manner.
Typically, the exhaust gas would be discharged to the ambient at a
lower temperature than either a gas turbine or diesel engine due to
the power extracted at the power turbine 26.
The rotary engine 24 forms the core of the compound cycle engine
system 10. In a preferred embodiment, the rotary engine 24 operates
with its compression ratio lower than its expansion ratio, which is
known as the Miller cycle, such that the exhaust and intake
pressures are held to similar values (within approximately 0.5
atm.), and with a high temperature engine block cooling system. As
shown in FIG. 2, the rotary engine 24 has an eccentric shaft 54 and
a rotor 56 which moves within a housing 58. The rotor 56 may be
connected to the shaft 54 by any suitable gear arrangement known in
the art. The rotary engine 24 has an inlet port 52 for admitting
air to the interior of the housing 58, a fuel injection port (not
shown) for delivering fuel into the housing 58 after the charge air
has been compressed and an exhaust port 50 for exhausting a gas.
Fuel is delivered into the combustion chamber such that the chamber
is stratified with a rich fuel-air mixture near the ignition source
and a leaner mixture elsewhere. The fuel-air mixture may be ignited
within the housing 58 using any suitable ignition system known in
the art. In another embodiment, fuel and air would be mixed outside
the engine and delivered as a pre-mixed charge to the inlet port
52.
The engine cycle 10 may be provided with a block cooling system 39
which has a fan 41, a coolant heat exchanger 40 connected to the
intercooler 22, and a coolant heat exchanger 42 connected to the
rotary engine 24. Running the block cooling system 39 at a high
temperature results in a lower weight cooling system and keeps more
heat in the cycle. This is especially important in the compound
engine cycle where rotary engine exhaust gases are used to power
the downstream turbines. Turbine performance is enhanced by
supplying exhaust from the rotary engine 24 at a pressure close to
the inlet pressure. Performance of the rotary engine 24 is enhanced
by supplying intake air from the compressor 16 at a pressure close
to or slightly greater than the exhaust pressure. Miller cycle
operation of the rotary engine 24 is important as it allows the
engine to accept intake air at a pressure of similar magnitude to
the high exhaust pressure caused by the downstream turbines. In
some applications, it may be desirable for the rotary engine
exhaust pressure to be either higher or lower than the inlet
pressure. The ability to independently tailor the compression and
expansion ratios of the rotary engine 24, as enabled by the
implementation of the Miller cycle allows the rotary engine exhaust
pressure to be chosen for the optimal combination of overall system
power to weight and SFC.
The Miller cycle can be implemented in the rotary engine 24 by
moving the location of the inlet port 52 around the periphery of
the engine to the location 52' and to a different crank angle as
shown in FIG. 2. In a reciprocating diesel engine, the Miller cycle
may be implemented by delaying the intake valve closing event.
Thus, the rotary engine 24 simplifies implementation of the Miller
cycle by replacing complicated valve timing with a simple geometry
change.
One of the aims of the engine system 10 is to retain cycle heat in
the exhaust gas leaving the rotary engine 24. This is so the
retained heat can be turned into useful work in the turbine 18 and
the power turbine 26. The exhaust gases exit the rotary engine 24
at approximately the same pressure at which the inlet air is
supplied to the rotary engine 24, i.e. from 3.0 to 5.0
atmospheres.
The rotary engine 24 is preferably operated to drive exhaust gas
temperature to a range of from 1500 to 1800 degrees Fahrenheit.
This may be accomplished by using thermal barriers, high
temperature cooling and insulation, and/or Miller cycle port
timing.
It is desirable to limit the peak cycle pressure in the rotary
engine to a range of from 1200 to 1800 psia. The size of the engine
is determined by the expansion ratio required to drop the pressure
from this peak to the desired exhaust pressure. The inlet port
angle, relative to the exhaust port angle, can then be determined
to achieve the desired peak cycle pressure given the inlet air
pressure. This will generally result in an inlet port that closes
later than in ordinary rotary engines. With the increased inlet
pressure, the area of the inlet port may be slightly smaller than
the inlet port of ordinary rotary engines.
Typical inlet/exhaust angles for a non-Miller cycle engine compared
to a Miller cycle engine in accordance with the present invention
are shown in the following table. In the following table, the
angles refer to the angular position of the crankshaft relative to
its positions corresponding to either minimum chamber volume (top
dead center, TDC) or maximum chamber volume (bottom dead center,
BDC). ATDC means "After Top Dead Center", BTDC means "Before Top
Dead Center," ABDC means "After Bottom Dead Center," and BBDC means
"Before Bottom Dead Center."
TABLE-US-00001 TABLE I Exhaust Intake Port Intake Port Exhaust Port
Engine Type Opens Closes Port Opens Closes Conventional 3-35 deg
30-70 deg 70-75 deg 38-48 deg ATDC (side ABDC (side BBDC ATDC port)
port) Conventional 80-120 deg 70-90 deg 70-90 deg 48-65 deg
(Racing) BTDC ABDC BBDC ATDC (Peripheral (peripheral Port) port)
Miller Cycle 0-15 deg 115-140 deg 70-90 deg 38-65 deg ATDC ABDC
BBDC ATDC
The significant difference between a conventional rotary engine and
a Miller cycle rotary engine is the intake port opening/closing
timing. Other port events may be chosen within the conventional
range depending on the application of the engine.
It should be noted that the delayed intake port closing, smaller
inlet area, and thus even more delayed opening, allows much less
inlet charge to dilute the exhaust gas than in current practice,
this driving up the exhaust gas temperature.
The compression ratio of the compressor may be in the range of from
3.0:1 to 5.0:1 and, the expansion ratio of the turbine may be in
the range of 2.0:1 to 7.0:1. Suitable ranges for the internal
volumetric compression and expansion ratios of the engine are given
in the table below.
TABLE-US-00002 TABLE II Internal Effective Internal Effective Exp.
Engine Type Comp. Ratio Ratio Conventional 7.0:1-11.0:1 Same as
compression ratio Miller Cycle 2.0:1-6.0:1 7.0:1-11.0:1
It should be noted that a significant difference between a
conventional rotary engine and the rotary engine 24, is that the
Miller cycle allows having an effective compression ratio that is
fundamentally different than the expansion ratio.
The concept of the engine described herein is enhanced by a high
temperature block cooling system for two reasons. Foremost, the
block cooling system represents a significant fraction of the total
system weight. Also, the colder the coolant, the more heat that may
be conducted from the working gases into the coolant. The high
temperature block cooling system will drive weight out of the
system and retain heat in the cycle and thus increase exhaust gas
temperature. High performance cooling systems now operate near 220
degrees Fahrenheit. The rotary engine described herein will drive
the temperature up to 250 degrees Fahrenheit as this will retain
approximately 1.0 to 3.0% more heat in the cycle and is the
practical limit for ethylene glycol (the coolant of choice for good
heat transfer) to avoid vaporization of the coolant and dry out in
the engine block.
There are a range of applications that require propulsion systems
in the 500 hp to 3000 hp shaft power range. These include turboprop
aircraft, midsized manned and unmanned rotorcraft, military ground
vehicles (tanks and armored personnel carriers) and watercraft
(both military and pleasure marine). Current propulsion systems for
these applications sacrifice specific fuel consumption (fuel flow
rate per unit power) in order to achieve high power to weight or
vice-versa. The compound cycle rotary engine described herein
addresses these applications and may be used as a propulsion system
for these applications.
It is apparent that there has been provided a compound cycle rotary
engine which fully satisfies the objects, means, and advantages set
forth hereinbefore. While the compound cycle rotary engine has been
described in the context of specific embodiments thereof, other
unforeseeable alternatives, modification, and variations may become
apparent to those skilled in the art having read the foregoing
description. Accordingly, it is intended to embrace those
alternatives, modifications, and variations which fall under the
broad scope of the appended claims.
* * * * *